1. Field of the Invention (Technical Field)
The present invention relates to electrodeposition of materials of various elements and surface structures on finely divided metals and other conductive powders and resulting material compositions with selectively engineered properties.
2. Background Art
The battery industries currently utilize nickel metal hydride misch-metal powders, which are an alloy of nickel or titanium and one or more rare-earth materials, such as lanthanum, or mixture of the lanthanum group formed into a composite alloy. The alloy then is reduced from an ingot size to a particle in the size range of 5 micrometers up to 150 micrometers. This material is used for nickel metal hydride rechargeable batteries as the negative electrode of the assembly and as hydrogen storage media and purification.
Cyclic lifetime is critical in the technology of Ni/MH cells. Hydride-forming electrodes made of LaNi5 undergo severe deterioration of adsorption/desorption capacities during charge/discharge cycling and thus have short cycle lives. It has been known that substituting small amounts of other elements for both La and Ni can slow the deterioration. Unfortunately, attempts to prolong cycle life in this way produced undesired side effects in the form of decreases in hydrogen-absorption capacities, slow kinetics, and prolongation of activation intervals (intervals of initial charge/discharge cycling needed to achieve full capacities) and thermal inefficiency. Existing methods for improving the alloy composition include varying either the alloy composition of nickel or other metals, such as titanium, to the rare-earth composition, or to isolate the rare earth metals to provide a more specific crystal lattice in the misch-metal alloy. Such approaches have found substantial limitations in four areas. First, the mechanical integrity of the alloy becomes very weak when pure metal, such as nickel, is combined with the misch-metal, which basically crumbles during the hydrogen absorption/desorption phase of a battery""s recharging cycle. Second, the existing powders have high internal electrical resistance. Third, the existing powders have poor thermal conductivity. Fourth, the catalytic element necessary to dissociate hydrogen is inefficiently distributed through the alloy bulk instead of being concentrated at the material surface where exposure to the target species occurs.
The following patents are illustrative of existing alloy compositions and methods of making same having one or more of the deficiencies noted above: U.S. Pat. No. 5,905,004, to Sakai et al., entitled xe2x80x9cElectrode for Alkali Secondary Battery and Method for Producing the Samexe2x80x9d; U.S. Pat. No. 5,443,616, to Congdon, entitled xe2x80x9cMetal Hydride Composition and Method of Makingxe2x80x9d; U.S. Pat. No. 5,104,753, to Sakai et al., entitled xe2x80x9cHydrogen Storage Electrode and Process for Producing the Samexe2x80x9d; U.S. Pat. No. 4,717,629, to Ishikawa et al., entitled xe2x80x9cCompact of Hydrogen Adsorption Alloyxe2x80x9d; and U.S. Pat. No. 4,431,561, to Ovshinsky et al., entitled xe2x80x9cHydrogen Storage Materials and Method of Making Samexe2x80x9d.
The present invention provides alloy compositions and methods of making same that dramatically reduce concerns in the four problem areas noted above. That is, the invention provides alloy compositions with high structural integrity, low internal resistance, good thermal conductivity, and selective catalysis. Furthermore, deposition thickness and porosity can be controlled in the present invention. Finally, catalytic elements can be selectively placed at the powder composite surface for more effective dissociation of molecular hydrogen or diatomic hydrogen to monatomic hydrogen, which intercalates into the alloy crystal matrix.
The present invention is of a method of producing metal hydride misch-metal composite powders comprising: providing to a rotary flow-through electrodeposition apparatus a powder whose particles comprise one or more lanthanide alloy metals selected from the group consisting of titanium lanthanide alloy metals and nickel lanthanide alloy metals; and electrodepositing one or more non-lanthanide metals on the powder via the apparatus. In the preferred embodiment, the particles may be completely or only partially encapsulated by the one or more non-lanthanide metals. Crystalline catalytic elements (preferably one or more noble metals, most preferably palladium and/or platinum) may be deposited after the deposition of the one or more non-lanthanide metals. The one or more non-lanthanide metals preferably are one or more of nickel, copper, tin, and zinc.
The invention is additionally of a composition of matter produced by the above method.
The invention is also of a metal hydride misch-metal powder comprising a powder whose particles comprise an inner core comprising one or more lanthanide metals and a porous outer encapsulant comprising one or more non-lanthanide metals. In the preferred embodiment, the one or more non-lanthanide metals comprises one or more of nickel, copper, tin, and zinc, and the inner core additionally comprises nickel and/or titanium. The particles may additionally comprise crystalline catalytic elements on the outer surfaces of the particles. The crystalline catalytic elements are preferably one or more noble metals, most preferably palladium and/or platinum.
Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.